Accumulating Anthropogenic Effects: The Decline of the Ivory Gull

I have spent quit a bit of time in the Arctic working on an expedition cruise vessel, but the ivory gull was always more elusive than its glaucous gull, black-legged kittiwake or even Sabine’s gull relatives. There would be an occasional fly-by of the ship or a couple would be spotted huddling together on a floating iceberg. The only time I got a really up-close look at this beautiful bird was unexpectedly when one landed just a few meters away from me as I was sitting on a black-pebble beach at Ny-Ålesund on Spitsbergen. From the beach it entered the water, peddling past me, extending curious glances. The best photos in this article date from that encounter.

The‭ ‬ivory‭ ‬gull’s scientific name, Pagophila‭ ‬eburnea, offers a good introduction to this special bird: pagos is Greek for ice, while philos means ‘loving’, ebur is Latin for ivory, with eburnea meaning ‘ivory-colored’. ‭ ‬

These‭ ‬high‭-‬Arctic‭ ‬marine‭ ‬birds‭ ‬do indeed spend their lives on or near pack ice. They have on average the northernmost breeding grounds of all birds.

The completely white plumage of the 40-cm adult bird lacks the grey or black back of other gulls. The thick bill is blue-ish with a yellow tip, and the legs are black.

Its genus is monotypic, which means the ivory gull is the only member of its family. There are no subspecies and no fossil members of the genus known. Recent genetic analysis shows that Sabine’s gull is the ivory gull’s closest relative, followed by the kittiwakes.

Ivory gulls breed between late-June and August in colonies of 5 to 60 pairs, but in rare cases a colony can number more than 100 pairs. Egg-laying can occur from mid-June to mid-July, but pairs may not breed at all if food conditions are unfavorable.

They nest on the ledges of steep, inaccessible coastal or inland cliffs up to 300 m high, on broken ice-fields or on bare, level shorelines with low rocks. The nest is constructed of moss, straw, lichens, seaweed and other debris on a snow-free area of rock in which they lay one to three olive-colored eggs.

Outside of the breeding season the ivory gull associates with the edges of pack ice, occurring singly or in flocks of up to 20 individuals. Their migration starts in November, with the first birds arriving on the wintering grounds of the Bering Sea, southeast Greenland and the Davis Strait-Labrador Sea in December, where they live near polynyas, large areas of permanently open water surrounded by sea ice.

Their distribution is near circumpolar in the Arctic Sea, breeding from northeast Canada (500-700 individuals), through Greenland (900-2000 pairs), Spitsbergen (800-1500 pairs) and islands off northern Russia (1500-3000 breeding pairs on Franz-Josef Land, 5000-6000 pairs on Severnaya Zemlya and 1500-3000 pairs on the rest of the Kara Sea Islands).

Including non-breeding birds this gives an estimated total of 58100-77200 individuals.

The Spitsbergen population is probably decreasing. Few of the known colonies were occupied in 2006, and those that were occupied consisted of fewer individuals than previously reported.

Breeding has apparently recently ceased on Victoria Island in Russia, but other Russian populations are thought to be stable.

The species seems to be declining in the south of its Greenland breeding range, while in North Greenland the trends are unclear, but overall the population trend in Greenland is estimated to be decreasing with ivory gulls having disappeared from 13 known and three suspected breeding colony sites. Data collected aboard an icebreaker travelling between Greenland and Svalbard between 1988 and 2014 found six to seven times more ivory gulls each year before 2007 than after that year in the Greenland Sea.

The most dramatic decline is reported from Canada. Local‭ ‬ecological‭ ‬knowledge‭ ‬interviews‭ ‬and‭ ‬colony‭ ‬surveys in the early 2000s‭ ‬indicate‭ ‬an‭ ‬80%‭ ‬decline, from 2400 individuals in 1987 to 500 to 700 birds in 2002-2003‭ ‬nesting ‬in‭ ‬Arctic‭ ‬Canada‭.‭ Data on population trends before the 1980s are not available.

Ivory gulls are listed as Near Threatened by the International Union for Conservation of Nature (IUCN) since 2005, before that as Lower Risk/Least Concern. They are considered endangered in Canada and registered as a Category 3 (Rare) species in the Red Data Book of the Russian Federation.

The IUCN notes that “[t]his species has declined rapidly in parts of its range, but its status in other areas is poorly known. A number of factors are likely to be contributing to declines, including climate change, pollution and increasing human intrusion or hunting within breeding areas.”

Climate change could have resulted in changes in the conditions on their feeding, resting or wintering grounds, like more severe winters, changing sea-ice distribution and thickness. Human intrusion consists of illegal hunting in Canada and Greenland, oiling at sea, disturbance of colonies due to escalating diamond exploration and/or increased nest predation.

Most research has concentrated on – and the clearest results have been obtained from – investigations into pollution in ivory gulls:

– Concentrations of total mercury (Hg) in eggs of this species collected from Seymour Island, Canada, have steadily increased since 1976 to levels which are now among the highest measured in seabirds (Braune et al. 2006).

– Levels of PCB and DDT are higher in eggs of this species than in all other Arctic seabirds (Braune et al. 2007).

– A 2007 Norwegian-Russian study of ivory gull eggs from Spitsbergen and the Russian Arctic in which thirty-five eggs were sampled from one colony in Spitsbergen, two colonies in Franz Josef Land and one colony in Severnaya Zemlya, high contaminant levels were found in the ivory gull eggs when compared to levels in eggs from other seabird species, like glaucous gulls and black-legged kittiwakes. In particular the levels of PCBs (polychlorinated biphenyls) and OCPs (organochlorine pesticides), dominated by DDE (originating from the pesticide DDT) were high. (Miljeteig et al. 2009).

-Measurement of the mercury content from fresh and museum Ivory Gull breast feathers of 80 ivory gulls dating from 2007 to as far back as 1877 revealed that feather Methyl mercury concentrations were 45 times higher in 2007 than 130 years before, while, based on constant feather stable-isotope values, there was no significant change in ivory gulls’ diet over this period (Bond et al. 2007).

These studies suggest that the ivory gull’s decline in numbers results from declines in reproductive success from the exposure to mercury and other anthropogenic pollutants.

Anthropogenic contaminants released in temperate regions in the northern hemisphere reach the Arctic by various routes, such as atmospheric and oceanic transport. Naturally released mercury (Hg), for instance from volcanic activity, has always existed in the environment. Life has evolved and adapted to those low-level traces, but there are new human sources of mercury in the world – gold exploration, medical and electrical equipment, cement-production, the ash and smoke that comes from the burning of coal – that far exceed the levels nature has adapted to.

Coal-fired electricity plants in China are currently the main source for the release of mercury.

Polar‭ ‬regions‭ ‬serve as global‭ ‬sinks‭ ‬for‭ ‬mercury.‭ ‬In ice-bound regions mercury particles accumulate on the ice over the long winter months. When the ice melts in summer, all the mercury surges into the ocean at once at a time when biological activity is at its maximum, transforming mercury biologically into toxic methyl-mercury (MeHg).

Ivory gulls also regularly follow polar bears to scavenge scraps from their kills. The species will also be found feeding where dead cetaceans, walruses and other seals have stranded or are adrift.

This scavenging behaviour gives ivory gulls a ‭‬relatively‭ ‬high‭ ‬trophic‭ ‬position‭ ‬in‭ ‬marine food ‭webs and thus makes them particularly vulnerable to contaminations that may have had and will continue to have a long-term effect on breeding productivity.

A range of studies have found a clear relationship between high levels of contaminants and various impacts on high trophic level birds in the Arctic:

Next to pollution, global warming is probably the most important culprit in the decline of the ivory gull. Of all the Arctic seabirds, ivory gulls are most closely associated with sea ice. Ice forms an ecosystem in itself. In locations where fresh meltwater seeps into the ocean algae bloom and invertebrates come to feed, which in turn attracts fish. The ivory gulls’ dependence on ice makes them particularly vulnerable to its loss. If ice doesn’t form near where they’re breeding they might not be able to feed their chicks.

Canadian ornithologist Alex Bond said that mercury is accumulating in the ivory gulls about twice as quickly as it is in other Arctic animals and added that if the current trends continue, the bird is likely to be extinct in less than 50 years.